rubyなれてる人ならはまらないんだろうけど、fluentdでfluent-plugin-mongoを入れてつかおうかなぁと思って gem intall fluent-plugin-mongo して、fluentdを再起動したら下記のように言われるわけです。 **Notice: C extension not loaded. This is required for optimum MongoDB Ruby driver performance. You can install the extension as follows: gem install bson_ext If you continue to receive this message after installing, make sure that the bson_ext gem is in your load path